1. Field of the Invention
The invention pertains to conveyor belts commonly used for the freezing and cooking of foods and other processing applications, and more precisely to improvements that make such belts more resistant to fatigue cracks.
2. Description of the Related Art
Endless, self-stacking conveyor belts used in the freezing and cooking food industries are described in U.S. Pat. Nos. 4,603,776, 4,941,567, 5,190,143 and 5,803,232. Such conveyor belts comprise a plurality of interconnected links, each including two transverse rods and a pair of upward extending side plates. The two transverse rods are parallel and horizontally aligned and extend through holes formed near the lower edge of each side plate. Formed on one-half of the each plate is a laterally extending foot over which the ends of the two transverse rods extend. Formed on the other one-half of each side plate is an elongated slot through which one of the transverse rods from an adjacent link extends. During assembly, the end of the outer transverse rod, called an edge transverse rod, is inserted through the slot formed on the side plate of an adjacent link and then extended through the hole formed on the side plate and over the top surface of the foot. During manufacturing, both transverse rods are welded to the outer surface on each side plate and welded to the top surface of each foot. A mesh made of a plurality of loop members that extend between adjacent transverse rods and the side plates to further interconnect the links and to support products on the conveyor belt.
During use, adjacent links are loosely interconnected so that the conveyor belt may travel endlessly in straight and helical paths. It is well known that during use, fatigue cracks develop in the welded joints between the side plates and the transverse rods. When cracks are detected or when the conveyor belt breaks, the entire machinery must be taken off line at a substantial cost to the operator.
Research by the inventors have shown that the fatigue cracks are caused by the inwardly directed, radial forces exerted by the stacked upper tiers on the lower tiers on the conveyor belt when the belt is traveling in a helical path. During operation, the conveyor belt is under tension as it enters the helical path of the spiral. The tension creates radial forces that travel through each rod, stretching the belt and increasing its pitch. These radial forces are not dissipated until the diameter of the conveyor belt is sufficiently decreased. In order to accommodate the decrease in pitch on the upper tiers, the side plates on the lower tiers are bent inwardly which stresses the welded joints. Eventually, the fatigue limits of the welded joints and adjacent areas are reached and cracks are formed.
The problem of fatigue cracks and breakage of the welded joints between the side plates and transverse rods on these endless conveyor belts are well known in the industry. Attempts to address the problem have included making the transverse rods larger and out of heavy, stiffer material. Unfortunately, these changes increases the overall weight of the conveyor belt which places higher loads on the drive and support system and limit the amount of product that can be carried. Heretofore, the formation of fatigue cracks has not been alleviated.
It is the main object of the present invention to provide an improved endless conveyor belt less susceptible to developing fatigue cracks without significantly increasing the overall weight of the conveyor belt.
It is another object of the present invention to provide a method for easily modifying existing endless conveyor belts to reduce fatigue cracks.
The invention is an improved self-stacking conveyor belt that includes a plurality of interconnected links, each containing at least two transverse rods and two side plates fixed to the opposite ends of the transverse rods. Wire mesh material is disposed between the two side plates around the transverse rods and used to support material or product for air treatment. The side plates are rigidly fixed to the two transverse rods via three welded joints: a foot welded joint that attaches each transverse rod to the foot; an outside buttress-type welded joint that attaches each transverse rod to the outside surface of the side plate; and an internal buttress-type welded joint that attaches each transverse rod to the inside surface of the side plate. Heretofore, only the outside buttress-type welded joint and the foot welded joint have been used and thought to be sufficient.
The improved conveyor belt also includes each transverse rod having at least one bendable section that enables the transverse rod to bend when radial forces are exerted on the top edge of one or both side plates. The addition of an internal buttress-type welded joint between each side plate and at least one of the transverse rod not only strengthens the interconnection of the side plate to the transverse rod but also transfers the stress to the bendable sections on the transverse rods to accommodate deflection of one or both side plates. Both features eliminate fatigue cracks and greatly extend the lifespan of the conveyor belt.
Also disclosed herein is a method of strengthening an existing endless conveyor belt.